tire pressure

[redimpss5]

allright, i know this has been asked before, but i missed it. tire manufactures always say check pressure when cold. i notice when i auto-x or goto the track, tires always inflate. i am going to vegas where its hot and wondered, how much air pressure should i inflate too, knowing they might will inflate?

[marzo7]

The standard answer is simply to stick with the manufacturer's recommended cold pressure as stated on the door jamb or owner's manual. For track use, you'll often hear people say to inflate tires to the maximum stated on the tire's sidewall. As noted in a thread below, the tire manufacturers are extraordinarily conservative in their listed "maximum pressure - cold", so unless your driving includes a tour of the surface of Venus, you can rest assured that the air pressure in your tires will never increase to an excessive amount.

In the real world though, air pressure does make a huge difference in the way a tire performs. And here I mean "hot" air pressure - as I negotiate a hairpin corner at 35 mph (or turn one on my local track at 80 mph), I don't really care what my tire pressures may have been four hours ago as my car sat idle in the driveway. My concern is about how they perform now, and that means what I really care about is what pressure they are at now.

On my car (a relatively light front-driver), I've found that traction decreases sharply as (hot) tire pressures get past 44 psi or so. Below about 40 psi (again hot), handling is a little sloppy as the tire rolls too far over on its sidewall during extreme cornering.

So what's this got to do with a trip to Vegas? Here's what I'd do: Set your cold pressures as usual. If, during hard driving in the hot Vegas sun, you find that the tires are feeling a little greasy, pull over and check your pressures. If they've gone up significantly, try letting a bit of air out to see if that improves things. With experience, you should find that there's an optimum range of hot pressures for your car.

The concern with this approach is that the next morning you may find that your cold pressures are now dangerously low. If your day will consist of only around-town driving and grocery-getting, then you should probably put air back into the tires to get back to the manufacturer's recommended cold pressures. If, however, you plan on driving hard again, then you may decide to leave your cold pressure "too low", knowing that with some spirited driving (and increasing ambient temperatures) your tires will heat back up to the optimum hot pressure that you found yesterday.